Harmonics detection is a critical element of active
power filters. A previous review has shown that the Recursive
Discrete Fourier Transform and the Instantaneous p-q Theory are
effective solutions to extracting power harmonics in single-phase
and three-phase power systems, respectively. This paper presents
the operating principle of a new modulation function integral
observer algorithm that offers a fast solution for the extraction of
the fundamental current and the total harmonic current when
compared with existing methods. The proposed method can be
applied to both single- and three-phase systems. The observerbased
algorithm has an advantageous feature of being able to be
tuned offline for a specific application, having fast convergence
and producing estimated fundamental component with high
circularity. It has been tested with both simulations and practical
measurements for extracting the total harmonic current in a
highly efficient manner. The results have confirmed that the
proposed tool offers a new and highly effective alternative to the
smart grid industry.